Phase splitting network



Dec. 1, 1953 w. SARAGA 2,661,453

PHASE SPLITTING NETWORK Filed June 21, 1950 14 Sheets-Sheet 1 INPUT PHASE SHIFT NETWORK 2 flfilo PHASE 0 SHIFT 1 MODULATOR1 NETWORK q a INPUT V sm fit summon W V sm mt I V gos .0; UNIT AIANDAZ PHASE J SHIFT 2 MODULATORZ nsrwoxx Inventor.-

Attorneys.

Attorneys.

14 Sheets-Sheet 2 W. SARAGA PHASE SPLITTING NETWORK Dec. 1, 1953 Filed June 21, 1950 Dec. 1, 1953 w. SARAGA "2,661,453

PHASE SPLITTING NETWORK Filed June 21, 1950 14 Sheets-Sheet 5 x IO H50 4 /nventor;

- 9-W 1 y w A ftorneys.

Dec. 1, 1953 w. SARAGA 2,661,458

PHASE SPLITTING NETWORK Filed June 21, 1950 14 Sheets-Sheet Dec. 1, 1953 w. SARAGA 2,661,458

PHASE SPLITTING NETWORK Filed June 21, 1950 14 Sheets-Sheet 5 HE) 60 I lnv entor,

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Attorneys.

Dec. 1, 1953 w. SARAGA 2,6 ,458

PHASE SPLITTING NETWORK Filed June 21, 1950 14 Sheets-Sheet 6 o'oolbi wows- 0-007. l 00025 o-oo3 K I! l l H5O Z Attorn eya Dec. 1, 1953 w. SARAGA 2,661,458

PHASE SPLITTING NETWORK Filed June 21, 1950 14 Sheets-Sheet 7 i (I00) A, 5n na X Sn u k JP L. A n1\' 1 AS A FUNCTION OF U=U +jU i5 DESCRIBED BY THE FOLLOWING TABLE AND DIAGRAM I 0 r m: l/m ..co

u 0 K 4 K ........o U2 0 O JAK '/1K' ..KI KI BEST FORM OF EXPRESSION GIVING 8 AS A FUNCTION 0F X Attorneys.

Dec. 1, 1953 w. SARAGA 2,661,458

PHASE SPLITTING NETWORK Filed June 21, 1950 14 Sheets-Sheet 8 yn U X k sn-1)\ =snu, 1? 1 LET M sn" 7 X) ='T THEN lrwenfzwi- ALI/w Mic/mews,

Dec. 1, 1953 w. SARAGA 2,661,458

PHASE SPLITTING NETWORK Filed June 21, 1950 14 Sheets-Sheet 9 IN THE GENERAL CASE Attorneys.

Dec. 1, 1953 W. SARAGA PHASE SPLITTING NETWORK Filed June 21, 1950 14 Sheets-Sheet 1O /nv en tor.-

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Dec. 1, 1953 W. SARAGA PHASE SPLITTING NETWORK Filed June 21, 1950 14 Sheets-Sheet 11 W k W [FM/1J1, =[F 2/y2 1*' am A w: [ms/m fu mn W v DEFINITION OF k4 I+ k2 Inventor;

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Patented Dec. '1, 1953 UNITED STATES PATENT OFFICE Claims priority, application Great Britain June 23, 1949 4 Claims.

This invention relates to electrical networks of the phase splitting type, and intended to operate over a relatively wide band of frequencies. A phase splitting network is one which, from a single phase input signal produces at least two output signals of different phase. The design of such a network to produce a given phase difference between the outputs is not difficult when the input signal is of a single frequency, but the problem of design is much more difiicult where the input signals may lie in a relatively wide frequency band, and particularly if not only constant phase differences but also constant output amplitudes are to be obtained.

Wide band phase splitting networks of this kind are used for instance for single side band modulation, for frequency-shift keying, for polyphase broadcasting, and for the generation of deflection voltages for circular oscillograph traces. An important use of the invention is in single sideband carrier wave transmission systems, in which suppression of one sideband is obtained by combining the outputs of two modulators the input signals and carriers of which have 90 phase difference. The present invention is, however, of wider application and is directed generally to the problem of providing means for obtaining polyphase voltages with constant amplitudes and approximately constant phase differences over a wide frequency band.

In the design of impedance networks including reactances, it is well known and can be demonstrated mathematically that the phase shift difference as a function of frequency cannot be made completely fiat over a finite frequency range unless an infinite number of sections are employed; the use of an economically possible number of sections can result only in an approximation to the desired characteristic. The present invention enables the best possible approximation to be obtained when a given number of impedance or reactance elements are used, and in accordance with the invention the impedance elements of the phase splitting network are so chosen that a given condition, which is set out in more particularity hereinafter, is met.

For a complete understanding of the invention, it appears necessary to consider phase splitting networks with any number of design parameters, of any desired bandwidth and of any desired degree of approximation to the ideal performance, and in the following description, and the accompanying drawings this will be dealt with by consideration of the three aspects of network analysis, performance curve approximation and network synthesis.

In these drawings:

Figure 1 is a schematic circuit diagram of a phase splitting network of the general type to which the invention relates,

F1gure 2 is a schematic circuit diagram of a side band suppression arrangement, being one of the important applications of a network in accordance with the invention,

Figure 3 is a diagram showing the effect of a deviation from the required constant phase difference on the side band suppression arrangement in Figure 2,

Figure 4 is a graph indicating the nature of a Taylor approximation,

Figure 5 is a graph for use when the Taylor form of approximation is employed,

Figure 6 is a graph indicating the nature of a Tchebycheii approximation,

Figure 7 is a graph for use when the Tchebycheff form of approximation is employed;

Figure 8 is a diagram and table of information for use in manipulating Equations 10a and 10b, referred to hereinafter;

Figures 9, 10, 11 and 12 are further tables of values for use in evaluating certain functions, as will appear hereinafter;

Figure 13 is a circuit similar to Figure 1,

Figures 14 to 18 are circuits of alternative phase shift networks, and

Figures 19, 20 and 21 are circuit diagrams for use in connection with the design of dissipationcompensated networks.

7 Figure 1 shows schematically a phase splitting circuit consisting of two phase shift networks the inputs of which are in parallel. At this point the phase shift networks are assumed to be conventional all-pass constant resistance single lattice section networks with series arm reactances X1 and X2 and lattice arm reactances Ro /X1 and -R0 /X2 respectively. Then the phase shifts 81 and ,82 produced by the networks separately are given by tan l91=X1/Ro and so that the phase shift difference =l31-fl2 is given by comprises two phase shift networks of; whic the.

inputs are in parallel, andjthe outputs ofv which are applied respectively to two, modulators. the. carrier inputs to which have 90 phase differ ence. The modulator outputs are applied to a summation unit. If it is assumed that all am:- plitude and phase relations are exactly. asrea quired, as indicated in Figure 2, with the one exception that y is not exactly unity, it can be shown that the amplitude A1 of the wanted sideband and the amplitude A2 of the unwantedsideband are given by where. a is. the deviation of the phase difference 31-62 from 90, i. e.

fi1-B2'?- (f and A is the valuelof A1 for 5:0 and A is the. value, of A2 for 6:0. If y is given, 6 can be'obtameddirectly from 1/. by means of Combining Equatiqms 3a and 3b with 5, In and can be "obtained as functionsof y. The result has been plotted in Figure 3. It is impo rtant to t??? as. h ee' iq m t o leaves L1 and L2 unchanged and transforms 6 into -a.

Equation 2 is very similar to an expression occurrin'g'in the evaluation of; the insertion loss L of a lattice section filter'between a sourceresistance Rd and a load resistance R with series arm reactances XA and lattice arm reactancesX It is seen by comparing Equations 6b and 2 that 1/1! and y are formed in the same way from reactances Xx, Xa and X1. X2 respectively. This similarity has important consequences for the beequal to 0 at zv=0, and thenthe resultsof the 65, v x x i l den te y n a i ll e n ater hat. the order of; approximation can be deno tediby analysis and synthesis of phase splitting networks" and will be referred to hereinafter.

Network analysis For the purpose of network analysis and synthesis it is necessary to find the general characteristics of the function y defined by Equation 2 if y is obtained from physical networks. Since n {rm-ta i 82 =1: l

y 2 B2) fll tan fi2 it is convenient to start with a discussion of the characteristics of tan /2 81 and tan /2B2.

From Equation 1 it follows that tan 81 and tan /2532 as functions of the normalised frequency a: have to. satisfy Fosters reactance theorem; theyvhavafor instance, to be odd rational functions of at; all poles and zeros are simple and occur, at real frequencies; zeros and poles are alternating; at 22:0 and no other values than 0. or a: are. permitted. The degree of denominator and numerator of each expression differs by one.

y=tan (p1-s2 is a function of a less restricted character; like tan 51 and tan gg it is an odd rational function of a: which is zero or infinity at zero and infinite frequency, but its zeros and poles need not alternate or occur at real frequencies and the degree of denominator and numerator can differ widely.

This follows directly from Equation 7 and is, because of Equation 61), equally valid for y and 1/13. Dealing now with y only, since it is required that y is approximately equal to unity over a band from say a;= Ic to :c=l/ /k' ltis obviously not permissible to have any poles or zeros of 11 within thisband. On the other hand it has been seen that at x=0 and :r:=== y will be 0 or w and, therefore, y will tend. to deviate more and more from unity for very large and very small values of :c. It seems plausible therefore to recommend, that no polesor zeros should occur at real values of a: except at 0 and as such. poles or zeros would tend to increase the deviation of y from *"ullit y; the poles or zeros at 0 and should be of the first degree andthe degree of numerator anddenominator must then differ by one. It will beseenhereinafter that Taylor and Tchebycheif, approximations lead to expressions which are in agreement with this recommendation,

what follows. it i will be assumed, that. at

3 0 (This assumption. entails no loss f een ra s the l er po sible choice is, 1:90 at 1 0, ow v this ase /11. would,

ll w n dis on. Could, be ppl ed tel/y, h ch p o mates unity, as closely as does 11.)

Then y will be of the form t d)( i- 2?) -Ha?) (8 (redhead?) (wa e) where b a =O or 1 and where the constants- Q12, C s and dl (12?. y 2 positive. The highest degree of :c occurring in y the same number n.

Equationiiq can al so be written in the form ZA|J+AQZ2+ +A f +Bm+ +Bwv where all As and Bsare real. Animportant case arises when y as a function of IQg aJssymI met ca bout. eel. o -.=0,; h rai and are real and.

formation m al/x then leads to y 1/y if n is odd, but leaves :1; unchanged if n is even. Expressions for ya when y" is symmetrical are listed below for nvalues from 1 to 6 Approximation of the required performance curve It is now proposed to discuss methods for finding values for the constants in the expressions for 11 (Equations 8a or 8b or 80) such that y becomes a good approximation to unity in the .rangew= /l?to r=l./ /F. If another value for 11, say 1I=Z/0, is required, 3 has to be replaced in the discussion that follows by J/yo. Taylor and Tchebycheff approximations will be referred to.

Taylor approximations A Taylor approximation of the n-th order is characterised by the fact that there are n design parameters which have been so chosen that for a specified value of a, say 113:;0, y itself and the first (n1) differential coefficients .for 1'=1, 2 (n1) are the same for the required curve and the approximating curve. Thus the approximating curve approaches the required one more and more closely the higher the value of n.

If it is assumed that 170:1, then the Taylor approximation of the n-th order is given by yn=tanh n tanh- 1r (9a) By writing Equation 9a in the form (1+x)"-(1x)" (l+x)"+(la:)"

it will be seen that the highest degree of .2 occurring in 111; is n and that 1111. is an odd rational function of a:, symmetrical about a:=1 against a logarithmic frequency scale. By writing it in the form 1+y. (1+w) c) it can easily be proved (putting yn=1+e and ac=1+A) that the first n-l differential coefficients at m=1 are zero, as required for a Taylor nq d, as. V and 3 an the mits of the y- 6 range as Vi and l/VK then A as a function of 7c is given by v tanh r1. tanhvi (9e) which, as far as the functional relation is con- 'cerned is similar to Equation 9a. 9c is written in the form it will be seen that x as a function of can be represented as a straight line with slope l/n through the origin of the coordinate system for any n-value, if functional scales defined by the i/tanhfunction are used for and k. This has been done in Figure 5. In view of the functional similarity between Qfand 9a, Figure 5 also represents pm as a function of x, in other words Figure 5 can be looked upon as showing the same curves as Figure 4. It will be seen that if k is given, llog x] decreases with increasing n, i. e. the range of 7; becomes smaller.

For synthesizing networks which have the performance described by Equation 9a, the values of a: at which y=+7 must be found; reference will be made to this hereinafter. These values are given by If Equation.

Tchebychefi approximations A Tchebychefi" approximation is characterised by the fact that the maximum deviation occurring is a minimum. The theory of the transformation of elliptic functions very conveniently describes odd rational functions of a, symmetrical against a logarithm i c :t-scale about 00: 1, which over the range ac= /lc to =1/ /k approximate 11:1, within the limits /A and 1/ in the Tchebychefi manner. As stated above, such limits for y are equivalent to limits fimax and 5min=-max for the deviation 5 of the phase difference It from the required value and Elliptic functions are dealt with in a book by A. Cayley entitled Elliptic Functions, published by G. Bell & Sons, London, Second Edition, 1895. This is the standard work, and it is convenient to use Cayleys notation. With this notation, it can easily be shown that the Tchebychefi approximation of the n-th order is given by The highest degree of a: occurring in the rational function defined by Equations 10 a and 10b is n. Cayley uses the suffix Z for A and M to indicate that a second transformation from a modulus k to a larger modulus A is meant. For the purposes of this specification it is convenient to use in many cases the suflix n to denote the order of the transformation. Therefore, in order to avoid confusion, Cayleys sufiix Z will not be used. For the purposes of this discussion it is also con venient to denote A sometimes as 7611.. In Equations 10a and 10b u'is an auxiliary variable which is defined .byEquationlOb and y" is defined in terms Of-1t by-Equation 10. is :has been defined above. A and M can be derived from k as follows: K /K is a function of k,-say K /K=F(k) known in the theory of elliptic functions. il /A denotes the. same function of A so=thatn /ii='F(A). A can be obtained from k by means of the relation It will be shown that if k. is given, \log A] decreases with increasing n, i. e. the range of .10 becomes smaller. Furthermore K canbe found as a function of k, and A as the same function MA, from Hayashis tables. Then Mis given by M=K/A (10d) Thus A=kn canbe obtained for any k and n,

and, 1c being specified, n can be so chosen as to make Log /A, which denotes the maximumdeviationof [Log yl from.(), as smallas required. A as a function of k and n is represented in Figure '7.

Since Equation 10c isof the same form as Equation9f'it is again possible to draw the A curves as straight lines with slope l/n if linear scales for K /K and ii /A are used. It souldbe noted that in the case of Tchebycheif approximations the curves relating A to 10 (Figure 7) do not at the same time relate yn to It willbe seen that for .any given kand n-values the values of A obtained from Figure 7, i. e. for Tchebycheff apmations'for 11:1, 2 .'6 for an r range from L x/l? to 1/ /7e where k=0.003 areshown diagrammatically in Figure 6. For these diagrams the formulae given in Figure 8 have not been used.

Only the values at which 'maxima orminima of 1/ occur and those atwhich 1:1 have been evaluated numerically, and the curves have been so drawn as to go through these points. However, for 121:4 as will appear hereinafter a numerical check for a great number of'points has shown very good agreement with the drawn curve. The curves have an oscillatory behaviour, all maxima and minima occur at the y-values 1/ /A and \/A respectively, the value of A depending on the n-value and the k-value under consideration. For even n-values thereare /211 maxima, (n--2) minima, two intersections with the line /Aand n intersections with the line 11:1. For odd values there are /2(n--1) minima and (n-1) maxima, one intersection with'the line y=1/ /A, one intersection withthe line y= A and n intersections with the line y=1.

In order to be ableto plotthese characteristic points of y it is necessary to knowthe values of a: at which :ljn=f\/)\, 1 and 1/ /A. 'On the'other hand, inorder'to-be able to write an as a rational function of a: in the form of Equation 80 itis necessary to know the values of :c at WhiChj1ln=0 and yn= and the value of H inthe case of even n-values (see below). Lastlyin order to synthesize a network having a performance curve in accordance with y, the values of x at which y=+i must be found. All these-values of a: can be found from Equations a. and 10b by first invertingloa to finduas a function of-y and then subetitutmg this expressiondor .uinhiob. However, to simplify the :engineeringapplication of H=VWMn "(11) When dealing with 'Tchebycheff approximations it is often convenient to make use of the index law which is valid for these approximations. Let ynkr, k) denotethe n-th order approximation to 1111:]. over the as-range VI? to l/x/le and let kn denote the range of variation of we, k) i. e. y" varies between Vic: and l/WT Furthermore, let ymwn, kn) denote the m-th order approximation to 'Jm=1 over the ynrange vii-to 1N1 and let (1mm denote the range of variation of 11711., i. e. 11m varies between \/(kn)m and l/\/(kn)m. Then ym(yn, 7c") considered as a function of as when a: varies from V7? to I/VI? is identical with 1/ !(1', k), the -p'-th order approximation to y =l, over the a:-range VI? to l/VE, if p=mn. This can be expressed -formally by :l/mQUn, kn) 11;:(17, p=

Mes -g in the case of 100. This means that in both cases A=kn as a function of k can be written in the form where k2"(k) means the m-th iteration of the function kzUc). Here m-th iteration refers not only to integral values but also to fractional values of m since m=logz n is only integral if n is an integral power of 2.

It is not possible to interpret in the same way theapproximating function y as an iteratedfunction of is because yis not only a, function of k,

but. of .r'and k. However, if the concept of itera tion is generalised so as to apply'to functions of two variables, then can be regarded as m-th iteration of y2(:c, k) where m=logz n. This :will now be shown.

Since k) leads from two independent to one dependent variable, aniteration is onlypos- Slb1e if there is introduced a, second dependent variable, say an arbitrary function zinc, k).

Then it is possible to define as (112)" and (2a) the functions (1/2) =1/2(y2,22) and Furthermore it is possible to define iterated functions of 112 and 22 for integral as well as nonintegral values of m as functions yz :F(a:, k, m) and zz =G(:c, k, m) of three variables which satisfy the following relations.

Now if as arbitrary function 220:, k) is chosen the function lawn-which happens to be independent of x--it will be seen that the index law (Equation 12) can be expressed in the form of Equation 13 if m=1og2 n as before. In' other words: 11 and kn can be interpreted as the m-th iteration of 11/2 and k2 when regarded as a pair of functions of a: and is.

It is interesting to note that such an interpretation is also possible if instead of an approximation by arational function the approximation by a polynomial is under consideration. If y= is to be approximated by the polynomial in the range :nzto as=+ the n-th order Tchebychefi approximation is It is Alternative theory of Tchebychefi approximations So far the theory of Tchebycheff approximations has been discussed in terms of elliptic functions. This leads to the most concise and most general type of expressions. At the same time it must be realised that many engineers are unfamiliar with elliptic functions and that it is sometimes difiicult to get hold of good tables of elliptic functions. It is therefore important to note that it is possible to formulate the approximations purely algebraically, without the use of elliptic functions. In practice a combination of the two methods of approach, appropriate to the particular case under consideration, is sometimes the best choice.

The algebraic theory for n=2,4,8 is very simple indeed. Starting with n==2, y2=dz:c/1]:l: leads to the following relation for :c= /7c and x=1/ /k, y2=yzm1n=d2 /k/(1+Ic) and for 03:1, y =1l2 max= V2612.

The condition 112 min'yZmax leads to and dz=2/ /kz. With this value for d2, yz is the Tchebycheff approximation of the second order for the range It. The cases 11:4 and n=8 can be discussed by applying the index law. The results are tabulated in the table which is included in Figure 12.

For n=3 the derivation of an expression for ya is less simple. Starting with an expression of the form y3=Hx(AQ+ac )/(Bu+m which in order to be symmetrical about 03:1 simplifies to 10 it is necessary then to determine a so that, for a given range k, y behaves in a Tchebycheif mann er. Y is required to be equal to V} if x= /k; furthermore g] has also the value as a minimum value at an unknown :cvalue, say r=b. Therefore -vi=ie a+r /X(1+am ]/(1+a:c must be equal to (:c /lc (wb) /(1+aa:

Comparing coefficients there are obtained three equations: I

vi /H21), c=b +2b /T: and vX='b /7 If there is introduced a, a term used by Cayley, by means of b=\/lC/a, then Equations 14a and 14b determine a, a and A in terms of k (A can als be determined by means of tables of elliptic functions, or by means of a graph such as that of Figure 7). Thence b \/k can be found, and thus 11 is known as a function of III, and also the following details:

If in the discussion of the case n=3 the independent variable a: is replaced by the 2nd order approximation m and k by K2, a 6th order approximation is obtained, and by repeating this process a 12th order approximation is obtained. If in the discussion of the case n=3, :1: is replaced by ys and k by k3 the 9th order approximation is obtained. For the prime numbers n=5, 7, 11 etc., however, the algebraic theory becomes'progressively more diilicult.

Network synthesis At this stage .it will be assumed that in one way or another a suitable performance function z/(zv) has been determined. The next step is the determination of two phase shift networks which will produce this function y. The problem to be solved is to find F0 andis known. As this problem occurs also in the design of symmetrical filters where (see Equation 622) is given and XA/RD and XB/RU have to be found as physically possible reactances, that solution can be applied to the presentproblem. S. Darlington in Bell Monograph B-1l86 Synthesis of reactance 4-poles which produce prescribed insertion loss characteristics gives the following instructions for determining the reactances (modified here in accordance with the symbols herein used): Write y in theIform y=xB /P where B and P are polynomials in :12. Then express P+pB in the form (PH-9B1) (P21JB2) where ,Pl, B1, P2, 1132 are ee'ven polynomials in p 4$, *such that theroots oi PL+IJBL== are the these values, say r criflthe, phase shift diflference I 'V QBi-Bi) approaches 44" which 'mustlbe due to fii tending towards +7 or pz tending towards -1 .Now that the two basic phase shift networks .withseries reactances X1 and X2 (see Figure 1) consist of elementary phase shift sections in tandem, each section being characterised by its *phase shift 3 and its normalised series arm reactance dx=tan p or-its normalised. series arm inductance 6.

Such elementary sections arej.indicated in Figure 13, which'is'a network of the type shown in Figure 11, and in whichthe .reactance values are as shown. In passing itmay be pointednoutthat in the general case of breaking-down .a phase shift network in-this way theindividuald-values obtained are. not necessarilyreal [but may occur in conjugatecomplexpairs. Thenthe two corresponding elementary sections can be combined to one physical section with normalised 'series arm reactance am/ (1--.bxi) :where .a.= 4b. However, inthe case of ,phasesplitting networks, complex a=values do not ocurc if a Taylor or Tchebyscheff approximation isiusedfor the performance'curve, and'they do' not seem to occur in other good approximations. On "the other hand, their occurrence is'therule in filter design.

,In Figure 6, at eachr; 'one'o'fthese elementary phase angles p'must" tend to +1? and That sign which makes d, the normalised inductance, positive is selected. If, in order to obtain a positive 11 it is necessary to take the positive sign, the corresponding B'isa constituent of 31, whereas in the other case there is obtained a constituent of B2. In this way not only are Xrancl X2 found, but-'als atthesame time, the constituent elementary sections .forming the two basic phase shift networks. It can be shown that forming the expressions "for X1 andXz .irom the inductances of :the :elementary :pha'se shirt sections in accordance with the addition theorem of the tan-function leadsto the expressions given by Darlington.

It will be seenthatn elementary sections lead toan expression tony in which .the highestdegree of a; is .n, and vice .versa. Thusthenumber of network elementsincreases with the. highest degree of a: occurring.

Practical design examples it is considered tha iiniselec ms p c a amples' it "is best ,to"'take simple "ones, as then the .method :of obtaining the networks can "be shown mo'stclearly. The-first example will be a casein which a Taylor approximation is required,

"selecting asimple cacaanamelyzmfliThenithe best approximation-is, given by Bari-"2 (see Equation 9d). .Bince n odd, thenumbfl' of sections of the two .phase shifting networks must differ-by one. Assume that the network with X1 consists of twosections-say withseries arm inductances (i1 and dz respectively. Then the network with X2 has'one single section,'say

By substituting a cubic equation is obtained for lis with one positiveroot: d3=+1. Then and X1 and X2 can be interchanged. 'In a more complicated. case the equation i y=+i would be solved to obtain the three'roots .r=i, a:=+:i(2+ and either by means of Equation or algebraically. In view of the signsof theroots'the first one must correspond to X2 and the other two must correspond to X1. Thus d1=='2+ c'tz=2 and d3:+1 are obtained as before.

The second example will be a case in which a Tchebychefl approximation is required, taking 121:4 so that analgebraic method can be used as well as thetrans'formation of elliptic functions forobtaining the'network elements. The specifled r-range is assumed to be from x= /ic to m=1/ /k where k=0.003. This corresponds to a frequency range from 30 cycles to 10 kc. Then lay-means o'f Hayashis tables k4=x is found to be 0.5959. The y-curve is shown in Figure 6. Table II'gives the expressions for the four .r-values at which -y= +7. 'Then using Milne-Thomsons tables, the followingvalues are obtained.

Then *for one phase "shift network dr=2.469, d2=0.05618;and for-the other. network (14:1/ d1=0.4049. From these values of d1, (22, da, 64 are found:

Xacanbe interchanged. .Applying the algebraic as before.

Alternctifivev phase shift networks The foregoing has'been'based on conventional constant resistance phase shift networks with 

